With development of HF EPR spectrometers around the world, there is an urgent need for samples which can serve as suitable and reliable sensitivity standards. We are exploring the possibility of using a Mn2+ impurity signal from MgO powder. Currently, the same sample has been studied using a HF EPR spectrometer at the University of Nijmegen, a 95-180 GHz spectrometer built at the Univ. of St. Andrews, and the 95 GHz EPR spectrometer at the IERC. It is anticipated that this international collaboration will facilitate both development of HF instrumentation and new standards for HF EPR.